Method for producing a detachably connected container having barrier properties

ABSTRACT

A method is provided of forming a multi-pack container assembly having at least two containers joined together by a channel. The method includes the steps of providing sheet having a barrier layer thermoforming the sheet into a multi-pack container assembly having a plurality of containers wherein each container comprises a flange and the flanges of adjacent containers are connected by an engineered area of weakness or channel. Resultant containers can be used for low-moisture, shelf-stable, ready-to-eat food products.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a detachably connected multi-packcontainer assembly having barrier properties.

2. Description of Related Art

Multi-pack container assemblies for storing several separate items areknown. Individual servings of refrigerated food products such as yogurtand pudding, and many other products can be packaged individually insuch multi-pack container assemblies. These multi-pack containerassemblies typically include several containers that are joined togetherto form a pack of individually sealed servings. Consumers will know thateach container can be separated from the multi-pack so that items in thecontainers can be used.

Typically, conventional multi-pack container assemblies are made bythermoforming polystyrene. Thermoforming is a widely known process formaking containers well known to those skilled in the art. Inthermoforming, a sheet of thermoplastic resin having a thickness can beclamped into a clamp frame and heated. An oven or heat station heats theedges as well as the center of the thermoplastic sheet so that when thesheet is subsequently delivered to a forming station, an overalltemperature balance has been attained. On being heated, the sheet isconveyed to the forming station where by one of several methods it isforced over a mold. The thermoforming of the polyolefin sheet can beperformed by means of different, conventional techniques, for instance,a vacuum can be applied in the mold and/or a counter mold can be used tohelp form the sheet into a container. The residual heat of the plasticcan be removed after forming. After cooling, the end product is removedfrom the forming station and sent to a trim press where the end productis trimmed from the web.

One disadvantage of polystyrene is that is has poor moisture barrierproperties. Thus, while polystyrene works well for refrigerated fooditems such as yogurt and pudding, polystyrene containers are undesirablefor items such as low moisture snack foods that require a containershaving moisture barrier properties. Unlike polystyrene, polyolefins,such as polypropylene, have excellent moisture barrier properties.

One drawback of using polyolefin containers such as polypropylene isthat polypropylene has a high tear strength. Tear strength measures thetear resistance of a material. Because of the high tear strength ofpolypropylene, it is commonly used in “living hinges.” A living hinge isa flexible hinge of plastic that is molded as one piece with the rest ofthe container or package, connecting the sturdy top and bottom sections.The material properties of the polypropylene permit the hinge to beflexed repeatedly over time without cracking or breaking. Thus,polypropylene packages are not conducive to detachably connectedmulti-pack assemblies. Consequently, when its been desired to provide apolypropylene-based multi-pack container assembly, cardboard is used tobundle several separate containers together. The manufacturing processused to produce cardboard bundled individual polypropylene containers,however, is expensive. Material costs are higher because cardboard mustbe used in addition to plastics material. Further, assembly costs arehigher because separate cardboard handling machinery is needed to bundlethe individual containers together. Another disadvantage of cardboardbundled polypropylene containers is that a consumer must tear throughthe cardboard in order to get a container which separates the containersfrom one another. Once separated, containers are no longer stored aseasily as when bundled.

U.S. Pat. Nos. 5,543,104 and 5,409,127 disclose an injection moldedcontainer assembly made of high-density polyethylene (“HDPE”). WhileHDPE containers do have moisture barrier properties, HDPE lacks oxygenbarrier properties.

To enhance the shelf life of a food product contained therein, a plasticfood container must have adequate barrier properties to protect theproduct from the migration of moisture or moisture and oxygen into thecontainer. This is typically accomplished by combining, in a layeredarrangement, several polymer sheets, each sheet having distinct barrierproperties. The typical goal in constructing such container is toprovide in the aggregate a layered sheet container that can beconstructed at a minimal cost, and yet provide adequate barrierproperties to light, moisture, and oxygen without impacting the taste ofthe product in the container.

For example, EVOH has been found to be an excellent oxygen barrier thatreduces oxygen migration into plastic containers. EVOH has been usedsuccessfully in combination with, for example, polyethylene, orpolypropylene (PP), where the polypropylene or PP provide the moisturebarrier properties for the container. Another benefit of using EVOH incontainers for food products is its resistance to the migration of oilsand contaminates, either from other sheet layers migrating into theproduct or from the product leaching into the container walls. Forexample, when post-consumer reground (PCR) polyolefin resins are used asone of the sheet layers for a container, EVOH has been found to be aneffective barrier to prohibit contaminates from the PCR resin from beingleached into a food product that is placed in the container. An EVOHlayer has also been found to be an effective scalping barrier to preventthe absorption of oil and oil-soluble flavors from packaged food.

It is difficult to foresee how a container having a layered arrangementof polymer sheets can be made by an injection molded process, since suchprocess by its very nature fails to provide a layered arrangementbecause a liquefied plastic mixture must be injected into a mold,resulting in a mixture with no contiguous oxygen barrier layer. Further,the capital costs associated with injection molded items is relativelyexpensive. Consequently, a need exists for a method for making adetachably connected multi-pack container wherein such container canprovide a manufacturer the option of a container having either moisturebarrier properties or moisture and oxygen barrier properties.

SUMMARY OF THE INVENTION

The proposed invention provides a method for making a detachablyconnected multi-pack container having barrier properties. In oneembodiment, the present invention provides a method for making adetachably connected multi-pack container assembly that can store lowmoisture shelf-stable ready-to-eat food products. In one embodiment,moisture barrier properties are provided by a polyolefin sheet. In oneembodiment, oxygen barrier properties are provided by an EVOH filmadhered to the polyolefin sheet. A channel disposed between the flangesof adjacent containers is provided to enable detachment of the adjacentcontainers such that unintended tearing occurring in the flange area isavoided. The above as well as additional features and advantages of thepresent invention will become apparent in the following written detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbe best understood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a perspective view of a thermoformed multi-pack containerassembly showing six containers in accordance with one embodiment of thepresent invention.

FIG. 2 is a cross-sectional schematic view of a multi-layered sheetincorporating EVOH in accordance with one embodiment of the presentinvention.

FIG. 3 is an end view of the multi-pack container assembly depicted inFIG. 1 showing an area of weakness between the flanges of the adjacentcontainers.

FIG. 4A is a blown up end view depicting the channel depicted in FIG. 3

FIG. 4B depicts another embodiment of the channel depicted in FIG. 4A.

FIG. 5 is a blown up top view depicting the channel depicted in FIG. 3.

FIG. 6 is a perspective view depicting the removal of a container fromthe multi-pack assembly depicted in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of a thermoformed multi-pack containerassembly 100 showing six containers 110 in accordance with oneembodiment of the present invention. Although the thermoforming processis known in the art, as used herein, the thermoforming process should beconstrued to include other equivalent processes including, but notlimited to, pressure forming and vacuum forming processes. Themulti-pack container assembly 100 comprises a plurality of individualcontainers 110 wherein the periphery of the top of each containercomprises an outwardly projecting flange 120. Adjacent containers 110are detachably connected by an engineered area of weakness or channel130 provided between the adjacent container flanges 120. As used hereina channel 130 corresponds to a thinned area between adjacent containerflanges that permits the containers to be separated. As used herein,“thinned area” is not a reference to a reduced area as a result ofscoring or perforations, but rather means that the channel thickness 132(as depicted in FIG. 4, discussed below) is thinned and is less than theflange 120 thickness.

In one embodiment, the channel 130 adjoins only a portion of thecontainer length and/or container width. Consequently, in oneembodiment, a portion 140 of the assembly 100 can be cut out or trimmedduring or after the thermoforming operation. In one embodiment, theportion 140 is cut out in the trim press after the containers have beenformed. Although FIG. 1 depicts the multi-pack container assembly ashaving six containers 110, the multi-pack container assembly cancomprise two or more containers. In one embodiment, the channel 130 canbe made in the trim press after the containers have been formed.

FIG. 2 is a cross-sectional schematic view of a multi-layered sheetincorporating EVOH in accordance with one embodiment of the presentinvention. In the embodiment shown, the outside polypropylene layer 212is adjacent to a post-consumer regrind resin 214 which is joined by afirst adhesive layer 216, such as a modified polyethylene, to an EVOHlayer 218. The EVOH layer 218 is then joined by a second adhesive layer220 to the interior post consumer regrind resin 222. The outermostproduct-side polypropylene layer 223 provides a moisture barrier layer.

The regrind 214, 222 can be made from a portion of the multi-layer sheetthat is cutout from the area depicted as numeral 140 in FIG. 1 androuted back into an extruder where it can be sheeting and co-extruded orlaminated in the multi-layer sheet that can be used in accordance withthe present invention.

In one embodiment, the multi-layer sheet comprises a material havingmoisture barrier properties adhered to a material having oxygen barrierproperties adhered to another material having moisture barrierproperties.

In one embodiment, the layer having moisture barrier propertiescomprises a polyolefin. Any polyolefin having a moisture vaportransmission rate of less than about 25 g/day/m²/mil (38° C., 90%relative humidity) and more preferably less than about 4.8 g/day/m²/mil(38° C., 90% relative humidity) has the requisite moisture barrierproperties that can be used in accordance with the present invention. Inone embodiment, the polyolefin having moisture barrier propertiescomprises polypropylene, and in an alternative embodiment, suchpolyolefin comprises high-density polyethylene.

In one embodiment, the layer having oxygen barrier properties comprisesEVOH. Any polyolefin having an oxygen transmission rate of less thanabout 1.92 cc/day/m²/mil (73° F., 0% relative humidity) and morepreferably less than about 0.4 cc/day/m²/mil (73° F., 0% relativehumidity) has the requisite oxygen barrier properties that can be usedin accordance with the present invention.

FIG. 3 is an end view of the multi-pack container assembly shown in FIG.1 depicting an area of weakness 130 or channel between the flanges 120of the adjacent containers 110. FIG. 4 is a blown up end view depictingthe channel depicted in FIG. 3. For simplification, the lidstock is notdepicted in FIG. 3 or FIG. 4. As shown by FIG. 3 and FIG. 4, the channel130 detachably connects the flanges 120 of adjacent containers 110. Thechannel 130 can be created by a flat die plate used in the thermoformingprocess. The channel 130 can also be created with a knife. The channel130 comprises a channel thickness 132 and a channel width 134. Thechannel 130 creates a way to control the tearing of materials such aspolypropylene that do not easily tear.

Referring to FIG. 4A, in one embodiment, the channel thickness 132 isless than about one-half of the flange 120 thickness. A largerdifferential between the flange 120 thickness and the channel thickness132 can help ensure tearing occurs in the channel 130 and does notmigrate into the flange 120. In one embodiment, the channel thickness132 is greater than about 1 mil. In one embodiment, the channelthickness 132 is about 5 mils. In one embodiment, the flange 120comprises a thickness of more than about 5 mils. In one embodiment, theflange 120 comprises a thickness of between about 10 mils and about 50mils before clamping in the mold and between about 5 mils and about 45mils after clamping. In one embodiment, the flange thickness is betweenabout 25 and about 35 mils before clamping and between about 20 and 30mils after clamping.

Although the illustration depicted in FIG. 4A shows the bottom of thechannel 130 as being flush with the bottom flange 120 of the adjacentcontainers, such configuration is shown for purposes of illustration andnot purposes of limitation. For example, the top of the channel can beflush with the top of the flange 120, or the channel can be stepped withthe both top and bottom of the flange. Such configurations are intendedto be covered by the scope of the present invention.

FIG. 5 is a blown up top view depicting the engineered area weakness orchannel 130 depicted in FIG. 3. Controlled tearing or separation betweenthe two flanges can be facilitated by a perforation. The channel width134 can be sized and shaped to permit a knife used for perforation toperforate the channel thickness 132. The channel width 134 can therebybe sized in accordance with the accuracy to which the knife or otherperforation means can be accurately placed into the channel 130 toperforate the channel 130. In one embodiment, the channel width 134 isgreater than about 20 mils. In one embodiment, the channel width 134 isbetween about 20 mils and about 100 mils. In one embodiment, the channelwidth 134 is created with the knife and comprises a channel width 134that is the same width of the knife making the channel 130.

The perforation can comprise any combination of cuts 136 and ties 138. Acut 136 penetrates the channel thickness and a tie 138 functions toconnect the two flanges 120 together. Such cuts 136 can be made at thetrim press after the containers have been formed. Referring to FIGS. 4A,4B, and 5, the channel thickness 132 can be manipulated as desireddepending upon several factors including the rigidity of the materialused, the ease of separation of the flanges, and the perforated or cut136 length, and the tie lengths 138. Similarly, the cut lengths 136 andtie lengths 138 can also be adjusted as desired in order to achieve thedesired amount of controlled tearing. The “percent of hold” is thepercent of material remaining uncut after a stock is perforated.Determining the optimum percent of hold is a function of the propertiesof the material and the channel thickness 132. The exact length of theperforations 136 can be obtained through experimentation. Thus, thevariables with the channel 130 including the channel thickness 132should be optimized so that when the containers are detached from oneanother a controlled tearing is achieved down the line of engineeredweakness and not into the flange area 120 of the containers.

Referring back to FIG. 4A, the channel depth can be defined as thedifference between the thickness of the flange 120 and the channelthickness 132. In one embodiment, the channel width 134 is substantiallythe same along the channel depth. Consequently, in one embodiment, thechannel 130 is substantially U-shaped. One advantage to suchconfiguration is that the perforation device can fall anywhere withinthe channel trough 130 and the thickness of the cuts 136 are going to besubstantially equal to the channel thickness 132 and are not as variableas would occur in a V-shaped channel.

A V-shaped channel 140 can be undesirable because the trough at the apexof the V 142 comprising the area of minimal channel thickness is a verynarrow portion. Further, because the amount of material to be perforatedor channel thickness 132 increases as a cutting device moves away fromthe trough apex or center 142 of the V-shaped channel 140, the abilityof a consumer to tear the polypropylene to remove a container from thecontainer assembly becomes more difficult. Further, the severed tielengths 138 can be sharper with an increased channel thickness which ishighly undesirable to consumers handling the detached container.However, a V-shaped channel 142 could be used if the accuracy of theperforating means was very high. Consequently, in one embodiment (shownin FIG. 4B), the channel 140 is substantially V-shaped.

In one embodiment of the present invention, the channel 130 comprisesone or more channel walls 124 where the flange terminates 122 at thechannel 130. In one embodiment, at least one of the channel walls 124 issubstantially perpendicular 122 to the flange. In one embodiment, thechannel 130 is substantially perpendicular 126 to at least one channelwall 124. In one embodiment, the channel 130 comprises substantiallystraight walls or walls that would be substantially parallel to thedirection in which a perforated cut is made.

FIG. 6 is a perspective view depicting the removal of a container fromthe multi-pack assembly depicted in FIG. 1. As shown in FIG. 6, thefirst container 210 can be flexed in a direction indicated by arrow 150to break apart ties 138 to produce a controlled tearing through thechannel 130 to separate the first container 210 from the secondcontainer 310. However, flexing is not required and a consumer canseparate the first container 210 from the second container 310 with meretensile force. Without the channel, tearing can be difficult to controland the flange 120 area of either the first container 210 or the secondcontainer 310 can be inadvertently and undesirably torn duringdetachment of separation of the first container 210. Such propagation oftearing into the flange area or onto the lidstock is undesirable as itcan cause an unwelcome mess and/or expose the food product toatmospheric conditions earlier than desired.

There are numerous advantages to the present invention. First, thepresent invention provides a method for making a detachably connectedmulti-pack container for shelf-stable, low moisture, ready-to-eat foodproducts. The present invention permits a multi-pack container that hasmoisture barrier properties and optionally oxygen barrier properties.Further, in one embodiment, the present invention produces a multi-packcontainer that can preserve and enhance the shelf life of food andnon-food, oxygen-sensitive items. Further, the present inventionprovides a multi-pack container made from a material that can beretorted. Consequently, food products needing hot fill or retortapplications such as dips or sauces including salsa and ketchup can bepackaged in accordance with the present invention. Secondary packagingtypically required for polypropylene or polyolefin type packages isthereby eliminated. Moreover, food products can be provided inindividual serving sizes that can be easily packed individually withlunches without requiring the opening of the food package and placementinto another package such as a plastic bag.

Second, as the product is consumed, packaging also disappears.Consequently, the notion of a “disappearing package” in the pantry canbe achieved whereby the amount of packaging left is commensurate withthe amount of food product left. Further, the food product staystogether and is unitized unlike packages connected by cardboard.

Third, a multi-pack container can be used in a thermoforming processresulting in higher cavitation and greater throughput than is currentlyallowed for single-serve polypropylene products that are individuallypackaged together in cardboard.

Fourth, the channel breaks up the area between the containers to helpensure the lidstock is more easily punctured and/or cut during theperforation step so that when the containers are detached the lidstockon the adjacent container is not torn.

As used herein, the term “package” should be understood to include anyfood container comprising a polyolefin sheet. While the layers andsheets discussed herein are contemplated for use in processes for thepackaging of snack foods, the multi-pack container can also be put touse for packaging of non-food products. While the invention has beenparticularly shown and described with reference to a preferredembodiment, it will be understood by those skilled in the art and thevarious changes in form and detail may be made therein without departingfrom the spirit and scope of the invention.

1. A method for making a detachably connected multi-pack assembly for ashelf-stable, low-moisture, ready-to-eat food product, said methodcomprising the steps of: providing a multi-layered sheet comprised of apolyolefin sheet having moisture barrier properties; thermoforming saidmulti-layered sheet into a detachable multi-pack assembly comprising twoor more containers, each container comprising an outwardly projectedflange, and at least one thinned channel connecting the flanges ofadjacent containers, wherein said thinned channel comprises a thicknessless than a thickness of said flange; filling said assembly with a foodproduct; applying a lidstock to said assembly; and perforating saidlidstock and said at least one thinned channel.
 2. The method of claim 1wherein said assembly comprises HDPE.
 3. The method of claim 1 whereinsaid assembly comprises polypropylene.
 4. The method of claim 1 whereinsaid assembly is comprised of an EVOH layer adhered to the polyolefinsheet.
 5. The method of claim 1 wherein said assembly comprises anoxygen transmission rate of less than about 0.4 cc/day/m² mil.
 6. Themethod of claim 1 wherein at least one of said channels is substantiallyU-shaped.
 7. The-method of claim 1 wherein at least one of said channelsis substantially V-shaped.
 8. The method of claim 1 wherein at least oneof said channels further comprises one or more channel walls when atleast one of said channel walls is substantially perpendicular to afirst outwardly projecting flange and a second outwardly projectingflange.
 9. The method of claim 1 wherein at least one of said channelscomprises a channel width greater than about 20 mils.
 10. The method ofclaim 1 wherein said channel thickness is less than about one-half of asaid flange thickness.
 11. The method of claim 1 wherein said channelthickness is greater than about 1 mil.
 12. The method of claim 1 whereinsaid flange terminates substantially perpendicular to at least one ofsaid channels.
 13. The method of claim 1 wherein said assembly comprisesa moisture vapor transmission rate of less than about 25 cc/day/m² mil.14. The method of claim 1 wherein at least one of said channelscomprises a channel width that is substantially the same along a channeldepth.
 15. The method of claim 1 wherein said polyolefin sheet furthercomprises oxygen barrier properties.
 16. The method of claim 15 whereinsaid polyolefin sheet comprises an oxygen transmission rate of less thanabout 1.92 cc/day/m² mil.
 17. The method of claim 1 wherein said flangecomprises a thickness of more than about 5 mils.
 18. The method of claim1 wherein said channel is created with a knife.
 19. The method of claim1, wherein said channel adjoins only a portion of the adjoining flangesof adjacent containers.